The present invention relates to the generation of tones or pitches for an electronic organ and is particularly concerned with a novel and simplified arrangement for obtaining the range of pitches necessary.
Most organs, at the present time, have one or the other of two types of tone or pitch generating systems incorporated therein. In one of the systems, twelve separate oscillators are provided, usually with associated circuitry for obtaining vibrato and the like. The other of the systems utilizes what is referred to as a top octave synthesizer, and which produces a range of pitches corresponding to the pitches employed in the uppermost octave of the instrument.
The top octave synthesizer generally employs a single high frequency precision oscillator, the frequency of which is divided down through a rather long divider chain arrangement to arrive at the pitches desired for the top octave.
The main disadvantage to the first mentioned system, in which twelve separate oscillators are employed, is that each oscillator must be tuned separately, not only in production of the organ, but also when the organ is tuned in the field. The tuning of such an organ is thus a complex and time consuming operation.
In the second mentioned system, namely, the system employing the top octave synthesizer, the problem of tuning twelve oscillators is eliminated, but the system is still quite expensive and involves an expensive precision master oscillator to obtain reliable results. The present day tendency toward embodying circuitry in large scale integrated chips presents problems in both of the systems referred to above.
The problems encountered in using a large scale integrated chip system are that pins provided for connections to the chip and the space available on the chip are both at a premium. When twelve separate oscillators are employed, twelve of the available pins, usually forty, of the chips are taken up thereby.
Fewer pins of the chip are required when using the top octave synthesizer system which is embodied directly in the chip, but the problem then presents itself that the top octave synthesizer is relatively large and develops considerable heat so that such a system embodied on a large scale integrated chip is also less than completely satisfactory.
With the foregoing in mind, a primary objective of the present invention is to eliminate the difficulties and problems referred to above.
In particular, an object of the present invention is to provide a pitch or tone generating system for an electronic organ which is less expensive than a top octave synthesizer system and which does not present the tuning problems that are encountered in connection with a more or less conventional twelve oscillator generating system.
A still further object is the provision of circuitry of the nature referred to which can easily be integrated in a large scale integrated chip and does not use an unreasonable number of the pins thereof and which circuitry can be connected with other circuitry which is smaller and which operates at a lower frequency than would be encountered in, for example, a top octave synthesizer system.